Sources: iPhone4 alone, iPhone4 with FiiO E17 using LOD, various computers using Audioengine D1 DAC and the D1's headphone out.

First impression of the Martin Logan Mikros 90 (abbreviated herein as M90): Slightly soft on the high end, and very soft on the low end. Unlike many modern headphones that are so soft on the high end they require a treble boost to play with hi-fi quality, the M90 would be satisfactory for me as is, except for the bass rolloff. I ran test tones for awhile to get a sense of the lower end, and the response rolls off at about 5 db per octave from 300 hz, so that 30 hz is down at least 15-20 db from the midrange. Compared to the B&W P5, the sound is very similar, with the P5 having a slightly softer treble and slightly more bass impact. The M90 has a fairly strong peak at 4 khz, and being squarely in the presence region, that probably accounts for the sense of a more lively high end (more presence) than the P5. Besides these things, the only other differences vary from track to track depending on where the major energies occur in those tracks.

The M90 is an on-ear headphone, with flat earpads very similar to the B&W P5 and P3, Bose QC3, Harman/Kardon CL, etc. The earpads are covered in a leather or 'pleather', and the headband covered in the same material with lots of padding. The M90 is all black except for a small amount of chrome trim. The simple metal tubes that hold the earcups are friction-operated with no click-stops. The earcups rotate 90 degrees one way to the flat position, but rotate only a couple degrees beyond parallel the other direction. The problem I had with the earcups is they didn't stay secure on my head even though I didn't move around, because the left earcup kept trying to rotate past the position I wanted it to remain in. The very thin and detachable cable has Apple controls, and since the connection to the left earcup is quite recessed, the plastic sleeve ahead of the metal miniplug cannot be thicker than ~6.25 mm. A very nice slim black zippered carrycase is included.

My opinion of the sound of the M90 is that it's good enough for high fidelity listening in genres that don't require much deep bass or bass impact. It certainly seems like an unusual signature for a modern headphone in the $300 USD price range. Because of that sound and the very modest build quality, I would judge the M90 to be better than several $100 headphones I'm familiar with, but not as good as several $200 headphones I have or have had. The $200 ATH ESW9a is a much better headphone in nearly every respect (lacking only a detachable cable), and even though the ATH M50 is bulkier and around-ear rather than on-ear, it offers a far better low end, and a high end that could be argued either way.

In other reviews I've done I've included the following music examples with comments about how the headphones sound with each track. My suggestion is instead of reading each one as an absolute unto itself, you could compare my notes here to other reviews and see how the M90 compares with each individual track.

Bauhaus - Bela Lugosi's Dead (~1980): Strong midrange sound effects - this is a good worst-case test for resonant-type sounds in the most sensitive midrange area. Handled pretty well by the M90.

Beethoven Symphony 9, Solti/CSO (1972): Excellent overall sound. Of special note for this headphone are the bass impacts beginning around 10:30 of the fourth movement. Those impacts are soft and well in the background, and you can barely feel the weight they carry.

Blues Project - Caress Me Baby (1966): Rarely mentioned, but one of the greatest white blues recordings ever. The loud piercing guitar sound at 0:41 into the track is a good test for distortion or other problems. Handled OK here.

Boz Scaggs - Lowdown (1976): Good sound quality - this is a great test for any nasality in the midrange. Handled very well by the M90.

Buffalo Springfield - Kind Woman (~1968): A Richie Furay song entirely, rarely mentioned, but one of the best sounding rock ballads ever. This will sound good on most headphones, and sounds good with the M90.

Cat Stevens - Morning Has Broken (early 70's): A near-perfect test for overall sound - this track will separate the best sounding headphones from the lesser quality types. Nothing specific, except that almost any deviation from perfect reproduction will stand out with this track. Sounds pretty good with the M90.

Catherine Wheel - Black Metallic (~1991): Goth with industrial overtones - I like this since it's a great music composition and the sound effects are smoothly integrated into the mix. This may sound distorted or mushy with some headphones, but the M90 renders the deliberate instrumental distortions clearly.

Def Leppard - Bringin' On The Heartbreak (1981): MTV goth/pop/metal at its best - good ambience and high energy - the better headphones will separate the details and make for a good experience. Lesser quality and the details tend to mush together. The M90 plays this fairly well.

J.S. Bach - E. Power Biggs Plays Bach in the Thomaskirche (~1970): Recorded on a tracker organ in East Germany, the tracks on this recording have the authentic baroque sound that Bach composed for, albeit the bellows are operated by motor today. The M90 plays the tones pretty well through the upper limits of the organ, which cover nearly the full range of human hearing. Of special note are the pedal notes - tracker organs have low-pressure pipes and don't typically produce the kind of impact around 30-35 hz that modern organs do. A headphone that's lacking in the low bass will sound especially bass-shy with this type of organ, and the M90 does sound a bit light here.

Jamming With Edward - It Hurts Me Too (1969): Intended originally as a test to fill studio down time and set recording levels etc., this was released a few years later for hardcore Rolling Stones fans. Although not as good technically in every aspect as the Chess studio recordings of 1964, and in spite of the non-serious vocals by Mick Jagger, this rates very high on my list of white blues recordings, and sounds fairly good with the M90.

Jennifer Warnes - Rock You Gently (1992?): The strong deep bass percussion at the beginning of this track has been cited as a test for weakness or distortion in certain headphones. The M90 plays those notes with reasonable impact and control. Having played this track a number of times now, I'm impressed with the M90's bass detail throughout the track.

Jimmy Smith - Basin Street Blues (early 60's): This track has some loud crescendos of brass and other instruments that don't sound clean and musical on some headphones. The M90 provides very good reproduction. Listen particularly to the second crescendo at 15 seconds in, for maximum detail effect. I'd like to emphasize that these crescendos are probably the worst-case test I have for instrumental separation and detail, and the M90 plays them well.

Ladytron - Destroy Everything You Touch (~2009): Featured in The September Issue, this song has heavy overdub and will sound a bit muddy on some headphones. Sounds good with the M90.

Milt Jackson/Wes Montgomery - Delilah (Take 3) (1962): The vibraphone is heavily dependent on harmonics to sound right, and the M90 plays it very well.

Pink Floyd/Dark Side of the Moon - Speak To Me (1973): Soft deep bass impacts will be heard and felt here.

Rolling Stones - Stray Cat Blues (1968): Dirty, gritty blues that very few white artists could match. On some headphones the vocals and guitar lack the edge and fall more-or-less flat. If you're a really good person, playing this song will probably make you feel nervous and uneasy.

Tony Bennett - I Left My Heart In San Francisco (1962): Frank Sinatra's favorite singer. Highest recommendation. With some of the best headphones, the sibilants on this recording are very strong, but they're not a problem with the M90.